Fire extinguisher apparatus



y 27, 1969 J. H. HOOK 3,446,287

FIRE EXTINGUI SHER APPARATUS Filed Oct. 19. 1966 Fl G. 2 l6 I7 H i 2 I8 if i r I I! F I G. 1

INVENTOR JOHN H. HOOK ATTORNEY United States Patent U.S. Cl. 169-28 4 Claims ABSTRACT OF THE DISCLOSURE A temperature resistant explosive cartridge assembly utilizing a jet of gas to break a frangible closure in a fire extinguishing apparatus.

In fire extinguishers and other devices utilizing a container of fluids under high pressure, a means for the rapid release of these fluids is necessary Previously, assemblies incorporating an explosively powered projectile to fracture such containers have been used for this purpose. These assemblies have proved deficient, however, in that the projectile often either leaves jagged edges or is itself lodged in the aperture which it forms, thereby impeding the flow of gases from the high pressure container. Further, the projectile can cause serious damage to the assembly from which it originates, thereby necessitating repair or replacement of the assembly.

A second type of assembly used for this purpose incorporates an outlet designed to burst upon the attainment of a predetermined pressure within the gas container. The primary disadvantage of this method of actuation lies in the time lag between the start of the actuating mechanism, e.g., the heat produced by fire, and the moment of release of the fluids contained within the vessel, during which time the bursting pressure is built up.

A further problem encountered with known assemblies of this type is that upon actuation, the electrical system which actuates these assemblies is often short circuited. Moreover, undesirable acutation may occur resulting from high temperature, impact, or stray electrical charges. Therefore, a need still exists for an explosive assembly adapted to the release of high-pressure fluids which is resistant to the high temperatures encountered in some situations in which such a device is useful, e.g., the engine compartments of aircraft; which is resistant to electrical charges to the extent that it will not be actuated by static discharges or elecromagnetic radiation such as are emitted by radio, radar, rotating electrical machinery, and the like;

which, upon actuation, does not short out the electrical 0 system to which it is connected, e.g., the electrical system in aircraft; which will release the high-pressure fluid contained in the vessel to which it is attached, efficiently, instantaneously, and with great reliability; and the actuation of which does not damage the fire extinguishing assembly to an extent that it is unusable after replacement of the explosive cartridge without additional repair or replacement of parts.

The instant invention provides such a cartridge which comprises a metal housing, a plurality of heat resistant explosive charges situated within said housing and a means for the independent electrical actuation of said explosive charges, said housing having a passage running from said explosive charges through one end of said housing. This cartridge is generally situated adjacent a frangible metal disc which serves as a closure to a vessel containing a fire extinguishing fluid under pressure, said passage being adjacent said frangible disc.

The ignition means used in the apparatus of the instant invention can be similar in construction to those com monly used in the art. These consist of an ignition charge in which are imbedded two electrical leads connected by a small bridge wire for actuation of this initiator. The ignition charge is preferably a deflagrating charge which is resistant to high temperatures, concussion, and small electrical discharges Those charges which are not actuated by the application of one watt of direct current power for five minutes or the application of one ampere of current for five minutes are preferred in the instant invention. Compositions which fall within the above requirements are referred to as having one-watt, one-ampere, fiveminute, no-fire characteristics. These compositions can consist, for example, of a mixture of magnesium, tellurium dioxide, and potassium perchlorate or of lead dinitro ortho cresol and magnesium. A mixture preferred for use in the instant invention consists of from 20-40%, and especially 33% magnesium, about from 60%, and.especially tellurium dioxide and about from 20-15%, and especially 17% of potassium perchlorate together with an inert dielectric binder having a melting point and decomposition above about 250 F. and preferably above 300 F. The quantity of said binder should be suflicient to form the ignition composition into a cohesive mass. Usually the binder comprises about from 1030%, and especially about from 10-20% of the mixture of binder and ignition composition.

The binder is preferably a polymeric binder, examples of which include vinyl resins including fluorocarbon polymers such as polytetrafluoroethylene, polychlorotrifluoroethylene and polyvinyl fluoride, polyvinyl acetate, acrylic polymers, and vinyl chloride polymers including homopolymers and copolymers of vinyl chloride; polyesters including polyethylene terephthalate as Well as styrene-crosslinked maleic acid polyesters; silicone resins and rubbers including alkyl-, aryl-, and alkoxy-substituted polysiloxanes; polyamides such as nylon 6,6; polyimides; and aminoand phenol-formaldehyde resins including phenol-, urea-, and melamine-formaldehyde thermosetting resins; epoxy resins; and mixtures thereof. Preferred binders are polyvinyl acetate and silicon rubber. After the combination of the ignition mixture and binder and its formation into an ignition bead, this bead is preferably coated with a mixture of silicone, cupric oxide and aluminum in a 20-6-2 parts ratio.

The explosive charge used in the explosive assembly can be any high-temperature deflagrating composition. These can include, for example, polynitroheterocyclic compounds such as tetranitro-2,3;5,6-dibenzo-1,3a,4,6atetraazapentalene and tetranitro-Z,3;4,5-dibenzo-1,3a,6,6atetraaza-pentalene; aromatic compounds of 6 to 7 carbon atoms bearing 3 nitro groups as the sole inorganic substituents (e.g., trinitrobenzene and trinitrotoluene); black powder, smokeless powder; lead azide; a mixture of tetranitrodibenzo 1,3a,4,6a tetraazacyclotetaene, potassium perchlorate, and magnesium; lead dinitro ortho cresol;

. lead dinitro ortho cresol, potassium perchlorate, and

smokeless powder; and tetranitrodizenzo-1,3a,4,6a-tetraazapentalene, potassium perchlorate, and magnesium.

Preferred for this use is an explosive composition comprising tetranitrodibenzo tetraazapentalene, potassium perchlorate, and a finely divided metal capable of rapid oxidation such as magnesium, aluminum and boron, of which magnesium is especially preferred. A mixture containing parts of tetranitrodibenzo-tetrazapentalene to 5 parts of potassium perchlorate and from 2 to 15 parts of metal powder is especially preferred for use in the instant invention.

The ignition means and the base charge are encased in an elongated cylindrical metal shell. The shell of the squib can be constructed of any metal or metal alloy Which can be readily formed into a suitable casing. This can include, for example, iron, aluminum, copper, tin, cobalt, nickel, and chromium, as well as the alloys of one or more of these metals, such as brass, stainless steels, and alloys of nickel, cobalt, and chromium. Brass and aluminum are especially preferred because of their malleability and consequent easy fabrication. The shell of the squib is preferably supplied with a coined bottom, e.g., a bottom the strength of which is substantially less than the other portions of the shell or, alternatively, no bottom at all. This facilitates the direction of the explosive force of the squib toward the passage in the casing of explosive assembly of this invention. The externalcasing of the explosive assembly can be made of any metal or metal alloy with suflicient strength to withstand the explosive force of the squibs within it without distortion. The group VIII metals, aluminum, tin, copper, chromium and their alloys are preferred, and aluminum is particularly preferred because of its great structural strength, light weight, and castability.

The present invention is explained in more detail by reference to FIGURES l and 2. FIGURE 1 is a cross section of a typical embodiment of the cartridge assembly in a fire extinguishing apparatus.

FIGURE 2 is a cross sectional view of the explosive load used in the assembly of the instant invention.

In FIGURE 1, 2 designates a cartridge case having a passage 1 at one end and containing two squibs 3 each of which has one of its leg wires 17 partially covered with a shortened length of insulating sleeve 5 and secured in potting material 4. This potting material can be an epoxy resin, and preferably an asbestos or glass filled epoxy resin such as Eccobond 104. Surrounding the space through which leg wires 17 extend is the terminal stud 14 which is partially covered by successive sleeves of insulator 6 and cap 7. Placed on the portion of terminal stud 14 extending through the outside of cartridge case 2 are insulating washer 9, metal washers 10 and 12, and nuts 11 and 13. A small amount of high temperature resistant solder 15 is inserted inside the inner diameter of terminal stud 14 and the threaded closure 8 between cap 7 and cartridge case 2 is locked by staking. The cartridge assembly is positioned such that passage 1 is substantially adjacent to frangible disc 16 of vessel 25, which contains fire extinguishing fluid. Ports 26 are provided to allow escape of the fire extinguishing fluid.

Cartridge case 2 is provided with passage 1 in the housing, which passage has a diameter, e.g., of on the order of 0.25-0.35 in., and preferably is immediately adjacent to the frangible disc 16. It is desirable that no damage occur to the fire extinguisher container or any of its parts for which the cartridge assembly of the present invention is particularly designed. The valve and the valve bonnet, i.e., the metal covering for the valve chambers, are especially susceptible to damage. To eliminate the possibility of this type of damage from the jet stream of gases produced by the squib or squibs, the cartridge is designed so that the passage 1 substantially contacts the frangible disc 16. The diameter of the passage 1 varies according to the size of the assembly, but is usually about from 0.25 to 0.35 inch and preferably about 0.31 inch and the gap between the passage 1 and the frangible disc 16 is less than 0.050 inch, preferably less than 0.025 inch. If the passage is in contact with the frangible disc, said disc should be greater in diameter than said passage, so as to allow the escape of the fire-extinguishing fluid. This passage serves dually to direct the gases produced by the squibs and to limit the space into which they can expand, thus causing pressure to build up faster. Insulator 6 and insulating washer 9 can be made of any insulating material. A laminated phenolic-resin plastic such as Phenolite or Lamitex is preferred in this invention. Two squibs 3 are utilized in the cartridge assembly of a preferred embodiment of the present invention so as to increase reliability. These squibs are independently wired so as to allow one squib to fire in the event of the failure of the other. However, when both squibs function properly, the cartridge blast will still not damage any part of the assembly so that it is serviceable through a number of consecutive firings.

In FIGURE 2, 24 designates a generally cylindrical shell containing a main charge 23 of high temperature deflagrating composition over which is a suitable amount of loose charge 22 of the same deflagrating composition. Sleeve 20 is inserted over loose charge 22, and ignition bead 21 having two leg wires 17 terminating within its center is placed in the center of loose charge 22. Plug 18 is inserted so that leg wires 17 extend through it and the entire assembly is held in place by crimps 19. The entire squib assembly is designated 3.

The squib contains a main deflagrating charge 23 of about from 12 to 22 grains of a tetranitrodibenzo-l,3a,4, 6a-tetraazapentalene and potassium perchlorate mixture, and especially 13.5 grains, of a 5/5/2 weight ratio mixture of tetranitrodibenzo-1,3a,4,6a-tetraazapentalene, p0- tassium perchlorate, and magnesium and a loose charge 22 of about 0.5 grain of the same mixture used in main charge 23. The leg wires 17 can be made of any suitable conductive material, for example, copper, silver, and iron, and preferably copper, and are not insulated.

That portion of the circuit within the ignition capsule comprising the bridge wire is preferably one having 0.35 to 0.45 ohm resistance. The metals from which the bridge wire may be made include alloys of metals of at least one of Groups VI(a) and VIII, optionally together with Group I(b) metals. Iron and nickel alloys, particularly those containing 50% or more of nickel or noble metal and noble metal alloys are preferred.

The explosive assemblies of the instant invention can be used to fracture a container of fluid under pressure. In this regard they are particularly useful as a component of a fire extinguishing apparatus. A typical apparatus of this type can comprise a vessel filled with a fire extinguishing fluid, for example, carbon tetrachloride, carbon dioxide, methylbromide, trifluorotrichloroethane or a mixture of two or more of the foregoing. The vessel is supplied with a small weakened area, preferably a frangible disc, the diameter of which is substantially equal to or greater than the diameter of the passage in the housing of the instant invention. The passage in the housing of the explosive assembly is situated substantially adjacent to the frangible disc. The electrical actuation of the squibs within the housing causes the force of the explosion to be directed through the coined bottom of the metallic casing, then through the passage in the housing toward the frangible disc, causing a fracture of the disc and the release of the fire extinguishing fluid within the vessel.

The following examples illustrate the present invention.

Examples 1-22 A number of cartridge assemblies are assembled as shown in FIGURE 1. The squibs used in these assemblies are similar to those shown in FIGURE 2. The squibs are prepared by placing three distinct increments of the main charge, consisting of a 5/5/2 by weight ratio mixture of tetranitrodibenzo 1,3a,4,6a-tetraazapentalene, potassium perchlorate, and magnesium in a bronze shell, 1.375 inches in length, having an inner diameter of 0.260 inch, an outer diameter of 0.272 inch and a coined bottom, 

